This invention relates to the manufacture of 1,3-diols from an epoxide. In one embodiment, this invention relates to the manufacture of 1,3-propanediol from ethylene oxide.
Glycols in general are valuable chemical compounds which find a wide variety of utilities. Such compounds are used, for example, as chemical intermediates in the manufacture of esters, as well as in the synthesis of polyesters. 1,3-Propanediol (1,3-PDO), also referred to as 1,3-propylene glycol or trimethyleneglycol, in particular, had been found to be especially useful in a number of applications. Typically, 1,3-propanediol has been prepared by acid-catalyzed hydration of acrolein to form 3-hydroxypropanal which is subsequently hydrogenated to the corresponding glycol. The high cost of acrolein and the relatively low yields obtained in such reactions have not led to commercial processes for production of 1,3-propanediol which are cost competitive with other commercially available diols which in many instances can be substituted for 1,3-propanediol.
The preparation of 1,3-glycols by the hydroformylation of epoxides, utilizing phosphine-modified cobalt carbonyl complexes as the catalyst, is shown in U.S. Pat. No. 3,463,819. In particular, said patent shows the production of 1,3-propanediol by hydroformylation of ethylene oxide, using a tertiary phosphine-modified cobalt carbonyl catalyst. Although high yields (92%) of 1,3-propanediol were claimed to have been produced in diethyl ether solvent, catalyst concentrations were extremely high, the amount of ethylene oxide charged was low, and no indication of reaction times nor reaction rates was specified. This high catalyst concentration may have been necessary because of the limited catalyst turn-over i.e.; 2-4 moles of product/mole of cobalt and phosphine. Yields of 1.3-propanediol were substantially lower in solvents other than diethyl ether.
U.S. Pat. No. 3,687,981 is also directed to a process for manufacturing 1,3-propanediol. However, the process disclosed in the '981 patent employs two separate stages. In the first stage ethylene oxide undergoes a hydroformylation reaction to produce hydroxyethyl hydroxy dioxane which is insoluble in the initial reaction solvent. The dioxane compound is separated from the initial reaction solvent and is subsequently catalytically hydrogenated to form trimethylene glycol. The patent generally discusses the possibility of using as the hydroformylation reaction catalyst, transition metals, particularly those of Group VIII of the Periodic Table, e.g., cobalt carbonyl tertiary phosphine and rhodium carbonyl. However, the examples in said patent are limited to the use of dicobalt octacarbonyl catalyst.
U.S. Pat. No. 3,054,813 is directed toward a process for the production of 3-hydroxyaldehydes or alpha-beta unsaturated aldehydes by the reaction of epoxides with synthesis gas. Said patent shows the use of a cobalt carbonyl catalyst for the hydroformylation of ethylene oxide, but the product which resulted was acrolein.
In an article by Yokokawa et al., Bulletin of the Chemical Society of Japan (Vol. 37, page 677, 1964), there is shown an attempt to hydroformylate ethylene oxide and propylene oxide using a cobalt carbonyl catalyst. In the case of ethylene oxide, the product was overwhelmingly composed of acetaldehyde. Small amounts of acrolein were formed. In the case of propylene oxide, under some conditions reasonable yields of 3-hydroxybutyraldehyde were produced, but the production of 1,3-butanediol is not mentioned.
It is likely that processes which produce 1,3-glycols from epoxides using "hydroformylation" catalysts, produce 3-hydroxyaldehydes as chemical intermediates which can either be hydrogenated to 1,3-glycols in situ, or isolated in some manner (as in the form of the aforementioned hydroxyalkyldioxanes) and then hydrogenated in a separate step. However, 3-hydroxyaldehydes, such as 3-hydroxypropanal, are unusually reactive species and readily undergo a variety of side reactions. In a literature review entitled "New Synthesis With Carbon Monoxide", B. Cornils, Springer Verlag, page 131, 1980, it was stated that numerous attempts had been made to subject oxiranes (epoxides) to the hydroformylation reaction to produce hydroxyaldehydes and that on account of the greater reactivity, not only of epoxides, but also of the resulting hydroxyaldehydes, the epoxide hydroformylation generally led to the formation of a mixture of products and thus unsatisfactory yields.
Under the conditions of a hydroformylation reaction, isomerization of ethylene oxide to acetaldehyde (which is sometimes further hydrogenated to ethanol) can occur. Furthermore, if hydroformylation of ethylene oxide to 3-hydroxypropanal is successful, the 3-hydroxypropanal can dehydrate to yield acrolein, which can be hydrogenated to propanal or propanol, or the 3-hydroxypropanal can undergo condensation (aldol) reactions with other aldehyde molecules to give C.sub.6 branched aldehydes, which can undergo dehydration and hydrogenation reactions. It is therefore highly desirable that a catalyst for the production of 1,3-propanediol from ethylene oxide should be able to rapidly hydrogenate 3-hydroxypropanal in situ before undesirable side reactions can occur. Such a catalyst would have the economic advantage of producing the 1,3-propanediol product in a single reactor, without the need for a large and expensive apparatus for the isolation and subsequent hydrogenation of aldehydes.
Thus, there remains a need for an effective method for manufacturing 1,3-glycols, especially from epoxides, which process is usable in a commercial manner.